Hadith Explanation about the Arrival of Apocalypse

Assalamu 'alaikum,
I remember reading a Hadith in Bukhari. The summary is:
Once a few rural barefooted people visit our Prophet (PBUH). They ask him, "When will Qiyamah arrive?"
Our Prophet (PBUH) then pointed to the youngest of the group and said, "Before he becomes old."
Our Prophet said those words nearly fourteen centuries ago, and I don't expect the man,our Prophet pointed to, to remain young till Qiyamah comes, because if he were young up to now, it'd have been known to us. I presume our Prophet meant something else by it.
Though I've only paraphrased the Hadith, I'm sure there's nothing more to it. I look for a clear explanation of it.
May Allah bless you.